306 THE PLANT COVERING OF OCRACOKE ISLAND. 



Ducts (probablj^ resiniferous) numerous, especially near the dorsal 

 surface, a^iparently always Ij^ing in the lilates of Avater tissue, one 

 below the leptome of the mid vein. 



Mestome bundles of the larger veins with a narrow (in transA'erse 

 section crescent-shaped) group of comparatively thin- walled stereome 

 above the hadrome.^ 



Aster tenuifolius L. 



Leaves narrow, almost vertical, isolateral, thick, with a deep groove 

 on the dorsal surface on each side of the midvein, margins slightly 

 incurved. 



Epidermis: Cells comi)aratively large, walls not undulate, the outer 

 greatly thickened; cuticle wrinkled and with slight furrows corre- 

 sponding to the radial walls of the epidermal cells ; stomata rather 

 few and large, the guard cells slightly sunken, mostly somewhat 

 deflected in direction from that of the leaf axis, bordered by usually 

 3 ordinary epidermis cells; hairs none. 



♦ Hypodermal collenchyma in a few narrow layers above and rather 

 wide layers below the midvein. 



CMorenchyma consisting of palisade with high, narrow cells, in 

 about 2 layers on both faces, strongly converging toward the mid- 

 vein, especially on the ventral side. 



Colorless parenchyma (water- storage tissue) occupying the interior 

 of the leaf in small quantity, and surrounding the midvein, where it 

 replaces the palisade. 



Mestome bundles not reinforced by stereome. 



Aster subulatus Michx. 



Leaves wider and thinner than in the preceding, almost vertical, 

 isolateral, flat, impressed above the midvein, which below is i^romi- 

 nent, with a furroA^^ on each side of it. 



Epidermis: Cell Avails not undulate, thick, the outer A^er}^ thick, 

 the inner collenchymatic-thickened A\^here hypodermal collenchyma 

 occurs; cuticle wrinkled; stomata, with guard cells lying parallel to 

 the leaf axis, level Avith the surface; hairs none. 



Hypodermal collencliyma above and below the A^eins (about 4 laj^ers 

 betAveen the leptome of the midA^ein and the dorsal epidermis) and in 

 the marginal angles. 



CMorenchyma, of compact palisade, occupying i^ractically the entire 

 thickness of the leaf except Avhere collenchyma occurs and about the 

 midA^ein. 



'The leaves of nonmaritime species of Solidago (e. g., S. petiolaris, S. neglecta, 

 and S. erecta) exhibit some interesting differences from S. sempervirens. All three 

 have bifacial leaves with compact palisade and open pneumatic tissue (chloren- 

 chyma least differentiated in S. petiolaris). Stomata few {S. erecta, S. neglecta) 

 or none {S. petiolaris) on the ventral surface, guard cells slightly prominent on 

 the dorsal surface. Hairs along the veins, especially on the dorsal face in S. petio- 

 laris, 3 or 4 celled sharp-pointed, bent. 



